Hello everyone

AC was not as cool as normal so decided to charge system. I felt the compressor was working before I started the charging process. However, I am not so sure anymore because when I jumped the pressure switch to keep compressor going during the charging process--the compressor did not engage. Could I have damaged something upstream at this time because suddenly I had no incoming power to the pressure switch anymore. Assuming as I said, I had power to that point before I started.

Beyond that question, Where does the power originate for the circuit which goes to the pressure switch. Is it protected by a specific fuse. (can not find a fuse for ac compressor wire (green with red stripe). Is there an ac relay for this model and year. I removed the glove box (no relay behind there)
Is a control which requires turning the knobs considered the manual climate control type. That is what we have.

If you can help with these questions it would be appreciated.

No power to pressure switch


Thanks Bill

Dear Bill,

Good p.m. and may this find you well. The A/C relay is inside the control box, on the front of which are the knobs, by which you select air flow and temperature (heat/cool). You will need to remove:
(a) radio
(b) storage compartment under radio
(c) air conditioning control box support bracket
(d) air conditioning control.

Inside the box, there is a printed circuit board (secured by four screws, if I recall correctly). The relay is black and rectangular. It has four legs. The solder joints fail, in invisible ways. If you reflow the solder, you likely will restore proper operation. Also reflow the solder on the main connector, which is directly behind the relay (12-14 connections).

Post back if you want more detailed guidance.

If you have a 25 watt soldering iron, you can do this. Use ROSIN core solder only (not acid core, which is used for plumbing work).

Hope this helps.

Yours faithfully,

spook

Hello spook

Thank you for taking the time to help. I am looking at an extra MCC which i picked up at a salvage yard. It is exactly as you described. I am going to remove the 4 screws and have a look. I have never soldered before. Tomorrow will be a first. Did jumping the pressure switch while the car was running cause a problem to the solder.

Thanks Bill

Dear Bill,

Good p.m. Jumping the switch with the power on is standard: without it, you can't assess the condition of the pressostat.

The solder joints fail, because they handle a lot of current (20-25 Amps). The failures can be microscopic.

As this is your first soldering job, I venture to offer a few thoughts:
(a) Use ONLY rosin core solder (the only type to be used for electrical/electronic work
(b) Use a low-power electric soldering iron (i.e., not a 100-watt gun), to avoid over-heating and damaging the board
(c) Make sure the tip of the iron is hot, by touching the end of your solder roll to it; the solder should melt at once
(d) To reflow a joint, you need only have the tip of the iron in contact with the joint for 1-2 seconds (about the amount of time it takes to say, "Saddam Hussein")
(e) work on the underside of the board, where the pins come through (easier to get at)
(f) The relay has four legs (if I recall correctly) and the main connector has 12-14 legs.
(g) Only add solder if a joint looks dry (i.e., if there is no, or very little, solder present
(h) wipe the tip of the soldering iron with a damp towel, to keep from dragging solder to places where it is not needed on the board's under-surface
(i) there is no need to disconnect the ribbon connector, that links the printed circuit board to the control unit.

Hope this helps.

Yours faithfully,

spook

Dear spook

Thanks again for the help

Bill